The Pirates' starting rotation took another hit Thursday when right-hander A.J. Burnett went on the 15-day disabled list with a strained right calf.

The move is retroactive to June 9. The team did not reveal when or how Burnett sustained the injury. Burnett was unavailable for comment.

“He made us aware of it (Wednesday),” manager Clint Hurdle said Thursday afternoon.

Left-hander Jeff Locke will start in Burnett's place Friday against the Los Angeles Dodgers. Right-hander Gerrit Cole remains set to pitch on Sunday.

The Pirates have not named a starting pitcher for Saturday's game. One option might be left-hander Andy Oliver, who is 3-2 with a 3.27 ERA at Triple-A Indianapolis.

Burnett, 36, is 4-6 with a 3.12 ERA and his .206 opponents batting average is sixth in the National League. He leads the league with 99 strikeouts and is tied for the lead with 14 starts. He ranks sixth in innings pitched (89 1⁄3).

Burnett's departure means four of the five pitchers who were in the starting rotation when the Pirates broke spring training camp are now out of action. Wandy Rodriguez (forearm tightness) and James McDonald (shoulder discomfort) are on the DL. Jonathan Sanchez was released May 8.

McDonald will make his next rehab start Sunday with Indy. Rodriguez (forearm tightness) threw soft and long toss Thursday and will do so again Friday. He is tentatively slated for a side session Saturday.

“Every team goes through these challenges throughout the course of a season,” Hurdle said. “We're in the middle of it right now.”

Contreras released

Reliever Jose Contreras was unconditionally released, which opened a spot on the 40-man roster for right-hander Charlie Morton (elbow surgery), who came off the disabled list Thursday and made his season debut against the San Francisco Giants.

Contreras tossed five innings over seven appearances and put up a 9.00 ERA. He allowed seven hits, walked six and struck out five. He went on the DL May 28 with a sore lower back.

Planet of the aches

Outfielder Starling Marte was scratched from the lineup due to soreness in his left rib cage. His status is day to day. ... Outfielder Jose Tabata (strained oblique) is in the early stages of a swing progression (hitting off a tee and underhand toss). He is tentatively scheduled to begin a rehab stint June 21. ... Reliever Jared Hughes (shoulder inflammation) remains in no-throw mode and continues in treatment and rehab. ... Righty Jeanmar Gomez (strained forearm) made a rehab outing Thursday with Indy.

Wilson hits rough patch

Rookie Justin Wilson has been hit hard in back-to-back outings. Sunday, he was tagged for three runs in 1 1⁄3 innings against the Cubs. Wednesday, the lefty allowed two runs in one inning against the Giants.

Wilson, 25, has pitched 37 1⁄3 innings, the most among NL relievers. Before Sunday, he had been charged with three earned runs in his previous 27 2⁄3 innings.

“I think it's just he set the bar so high so soon,” Hurdle said. “His numbers are going to (even out). You do have to monitor the role he's in. We've been very careful with the workloads. That's the challenge that comes at this level — sometimes, you've got to wear it and get through it.”

Thanks, veterans

All active military personnel and U.S. Armed Forces veterans can get up to four free tickets to the July 4 game against the Phillies. Tickets are available on a first-come, first-served basis — in advance at PNC Park ticket windows and at 11:30 a.m. on the day of the game at a kiosk on Federal Street.

10 draft picks sign

The Pirates announced the signings of 10 of their selections from last week's draft, including fourth-rounder Cody Dickson, a left-handed pitcher from Sam Houston State. He will be assigned to the team's short-season club in Jamestown.

Outfielder Gregory Polanco was promoted to Double-A Altoona. Polanco, 21, batted .312 with a .836 OPS in 57 games at High-A Bradenton. He collected 17 doubles, six homers and 24 stolen bases. ... Three players with Pirates ties — infielders Jim Negrych and Andy LaRoche and outfielder Brad Hawpe — are among the top vote-getters for the Triple-A all-star game. Negrych was drafted by the Pirates out of Pitt in 2006. Hawpe was in Pirates spring training camp this year, was released and then signed with the Los Angeles Angels. LaRoche was the Pirates' third baseman from 2008-10. No player from Indianapolis, the Pirates' affiliate, is listed among the leading vote-getters. Fan balloting will close June 26.

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